1. Field of the Invention
This invention relates to a method and apparatus for generating a plasma arc used for microplasma arc welding, arc transformation hardening of miniature parts, minute working, etc. 2. Description of the Prior Art
In the recent frontier technical fields, miniaturization of various device parts is required and also the development of welding techniques suitable for welding miniature parts having a thickness and a diameter each on the order of microns is desired in the field of welding art.
In order to weld miniature metal workpieces on the order of microns, electron beam welding, laser welding, and microplasma (needle arc) welding are used conventionally. The minimum weldable thickness of a plate-like (foil) workpiece at present is 20 microns (Published Examined Patent Application 3911/1985). The minimum weldable diameter of a wire is about 125 microns (E. F. Gorman et al.: Welding J., No. 11, 1966).
An electron beam welding machine and a laser welding machine are both expensive and difficult to use industrially while a microplasma welding machine is relatively inexpensive as a kind of an arc welding machine and easy to use.
However, the minimum current value available industrially at present to such microplasma arc welding is still 0.1 amperes with which, at most, the edges of lapped stainless steel plates 25 microns thick can only be welded and thinner plates (foils) are difficult to weld.
At present, a method of generating an arc current below 0.1 amperes in a stabilized manner cannot be obtained.